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2) Can such a bar be installed on any page of any website, or it has to be a blog or something?
The kind of site you have will affect the code you need. The key requirement in most cases is to be able to put the page URL into the script and perhaps other page variables, too. The best kind of link not only goes to a submit page but also populates it with at least the URL and page title.
I've seen a few compilations of these links, but most of them are for specific blog or CMS software. You could probably look for, say, a compiliation of WordPress links and modify them as necessary to integrate with your software.